Please explain the difference between these two risers, if you've had personal experience with both.  How close are these two risers in design?

The 3D riser is the standard riser with a narrower throat.  The JK riser has about 3/8-inch taken off the heel and the throat of the riser is larger than the standard riser, about 3/16 inches deeper front to back and about 1/8-inch side to side.  

Because of the small throat on the 3D riser, it's only warranted for weights up to 50#.

If you shoot with a higher wrist, you'll probably like the 3D riser.  If you like a lower wrist, that's what the JK riser is.

I have the new 3DH which is built for over 50 pounds. Mine is 51@27, 62". I love this riser, slim, positive and longbow like. Doesn't feel like a recurve with longbow limbs. Also doesn't hurt that this bow equals any recurve I've owned for speed with a 600 grain arrow.  . Frank

They also have a 3DH riser that doesn't have the 50# weight restriction as the 3D riser has.I like the looks of the 3DH riser,it has a lower grip like the JK riser.

Thanks. Ive wanted a JK low wrist, 64" A&H. I purchased a used 66" 45@28, 3D riser A&H CX. Great bow, just don't know if I like the really flat palm, locator grip of the 3D.